1. Field of the Invention
The present invention relates to a power source circuit, and, more particularly, to a power source circuit provided with a booster circuit and with switching an input voltage to the booster circuit without using a switching circuit.
2. Description of Related Art
In general, a device for driving a liquid crystal display needs a high voltage power source for driving a liquid crystal and this high driven voltage power source is generally provided with a booster circuit such as a DC—DC conversion system.
In this voltage power source for a driver of the liquid crystal display, two kinds of voltages, a first voltage V1 (2.6V, for example) and a second voltage VC (1.3V, for example), which is lower than the second voltage, are prepared as power source voltages and one of these two voltages V1 or VC is switched by using a switching circuit in order to form various voltages of response to loads in various functions of the liquid crystal display.
However, in the power source circuit for the driver of the liquid crystal display, the switching circuit for switching an input voltage is arranged in a former stage and a booster circuit is arranged in a latter stage such that there is a problem where an output impedance of the booster circuit is increased by an effect of a switching resistance from switching transistors constituting the switch circuit.
Therefore, in view of the above problem, the present invention is intended to provide a power source circuit that is capable of switching an input voltage into a booster circuit without a switching circuit and decreasing an input impedance of the booster circuit as much as possible.